Method of making hard alloys for cutting tools



Patented Nov. 28, 1933 UNITED STATES search Room METHOD OF MAKING HARD ALLOYS FOR CUTTING TOOLS Clarence W. Balke, Highland Park, Ill., assignor, by mesne assignments, to Ramet Corporation of America, North Chicago, 111., a corporation of Illinois No Drawing. Application March 26, 1930 Serial No. 439,228

Claims.

This invention relates in general to the production of alloys, and has more particular reference to the production of very hard alloys for use primarily in the formation of cutting tools,

'5' which will be sufliciently tough to resist crumbling and breakage.

The invention contemplates the provision of a very hard alloy, comprising a refractory metal, such as tantalum, carbon, and one or more metals of the iron group and having sufiicient toughness to make it particularly suitable for the formation of tools designed for cutting hard metals, such as cutting tools for lathes, planers, and other metal cutting and working machines. Me-

chanical strength sufficient to resist the reaction of the feed, hardness to a degree sufiicient to resist the wear under heavy cutting duty, tenacity or toughness to resist crumbling or breakage, and the retention of the foregoing qualities even at the relatively high temperatures developed in the use of the tool are the desirable qualities which have long been sought by metallurgists, and heretofore various alloys or compositions have been suggested as having these desirable qualities for the formation of cutting tools.

Alloys for the formation of cutting tools have heretofore consisted of various combinations of auxiliary metals with a refractory metal like tungsten or carbides thereof. While such alloys possess a high degree of hardness, they are more or less brittle and, therefore, are subject to crumbling and breakage in service. The degree of hardness and the tenacity or toughness of such an alloy depend upon the relative amounts of carbon and the auxiliary metal employed in forming the alloy, the purity of the metals composing the alloy, and the method used in forming the alloy.

It has been customary in the formation of such alloys to mix the powdered constituents of the alloy in the desired proportions and to press and subject this powder to a preliminary heat treatment to fuse the powders to a body, after which the alloy was formed to the desired shape and size. These formed bodies were then sintered and finished while hot. Upon examination such carbide alloys present a porous or coarsely granular section and have a tendency to chip or crumble when used as a tool for cutting hard metals, requiring, therefore, frequent grinding. A primary object of this invention is therefore to overcome these difiiculties by so making an alloy of the class hereinafter disclosed as to substantially eliminate this coarsely granular structure or porosity and thereby to produce an alloy suitable for use in the formation of cutting tools for hard metals, which will be harder, tougher, and more durable for any,given proportion of the constituents of the alloy.

An important object of this invention is consequently the novel method of making a substantially non-porous alloy which will be extremely hard and sufiiciently tough to prevent chipping or crumbling when formed as a tool.

Another important object of the invention is the production of a novel, hard alloy in which a metal carbide, having an excess of the metal of the carbide is so formed that this excess of the carbide metal is free to alloy with an auxiliary metal to provide a hard and tough composition.

Another important object of the invention is the provision of a novel method of so alloying a refractory metal carbide with an auxiliary metal that a cutting tool made of the alloy will be substantially non-porous and will be adapted to cut hard metals without chipping or necessitating frequent grinding.

Another important object of this invention is the provision of a novel method for producing a hard and tough alloy comprising a refractory metal carbide, and one or more metals of the iron group combined with the carbide.

Other objects and advantages of the invention will be apparent from the following description which discloses a preferred embodiment of the invention.

The novel method for producing the hard and tough alloy of the present invention briefly comprises uniting a refractory metal powder, from the groups including tantalum, columbium, molybdenum, or tungsten powder, with carbon which has been pre-heated to purify it. It will be understood that the oxides of these metals are here contemplated as within the scope of the present invention. The refractory metal oxides may be previously reduced in a known manner or united with an excess of carbon which serves to reduce the oxides, leaving enough carbon to form the desired carbide, having the theoretical amount 100 or less to form the refractory metal carbide indicated by its chemical formula, such as TaC. The tantalum-carbon composition is then heated in an evacuated electric furnace, and is ground to a very finely divided powder. This finely di- 105 vided powder is next mixed with a hydrogen reduced metallic powder of one or more metals of the iron group, and the carbide and metallic powders are very thoroughly mixed and ground to an extremely finely divided powder.

After thoroughly mixing the carbide powder with that of the metal or metals of the iron group and grinding them to a very finely divided form, the mixture is subjected to tremendous pressure to form the mixed powders into a body of the desired size and shape which may be handled. This body is subjected to a heat treatment in a vacuum at from 1350 to 1400 C. to combine the metal or metals of the iron group and the other constituents in the form of a solid, homogeneous alloy having an exceedingly fine grain and providing a very hard and tough alloy suitable for use in the manufacture of cutting tools and for other uses requiring an alloy combining the qualities of hardness and great tenacity or toughness.

Attention is here directed, before proceeding with the disclosure of the invention, to the tremendous pressure referred to above in forming the mixed and ground powders into a substantially non-porous and homogeneous body. This pressure is sufiicient to permit handling and readily forming the body to a desired shape and size prior to the heat treatment which combines the constituents of the alloy, and in practice, a pressure of about eighty tons per square inch is used.

Thus, the novel method outlined above elimi nates a step now common in the art which involves a preliminary heat treatment of the mixed materials after pressing in order to provide pieces of the alloy which can be handled and formed to shape, and finally heat treating after such forming to the shape desired.

In carrying out the invention to accomplish the above mentioned objects, it is desirable to provide an excess of the refractory metal to form the carbide although the exact theoretical amount to form the carbide of the refractory metal may be used when an alloy is desired, which is not quite so hard. Where tantalum carbide powder is used, the alloy has a characteristic yellowish or dirty brass color which persists in the final product of this novel method. This color may be said to be characteristic of tantalum carbide tools and distinguishes them from other tools.

The carbon employed to produce the carbide is preferably in the form of lamp-black or charcoal, which has been preheated in a closed graphite crucible to 1500 C. to volatilize any organic matter contained by the carbon and to rid it of objectionable gases. After such purification of the carbon, it is mixed with a refractory metal powder such as tantalum powder in about the proportion of from 5 to 6.2% and 95 to 93.8% Ta by weight, the mixing being carried out in a graphite crucible packed in lamp-black. This mixture of tantalum and carbon is then placed in a high frequency furnace and united by slowly raising the temperature to about 2000 C. and maintaining this temperature for about one-half hour to combine the carbon and tantalum to chemically combine the powders.

This step of the novel method is usually accompanied by a violent reaction. The tantalumcarbon composition that results from the foregoing uniting step is a tantalum carbide having from 5 to 6.2% by weight of carbon and has a dirty yellow color. The tantalum carbide is next ground in a ball mill for about twenty-four hours to a finely divided powder having the characteristic color mentioned above. After grinding the carbide, it is heated preferably in a tantalum vessel, to from 160D to 1700 C. in a vacuum furnace to degasify and to complete the reaction between the refractory metal and the carbon. This heating serves also to completely reduce whatever oxides that may be present in the carbide. The carbide powder may be subjected to sufficient pressure to hold the particles together under the action of the vacuum pump before the foregoing heat treatment. This also serves to reduce the air spaces among the particles of the powder. This carbide is then ready to be combined with an auxiliary metal for producing a homogeneous alloy. While this auxiliary metal may be any suitable base metal having a fusing or sintering temperature below the melting point of the carbide, which will alloy with the refractory metal used at a comparatively low temperature, the present embodiment of the invention contemplates the provision of one or more metals of the iron group, such as iron, nickel and cobalt. Preferably from 3 to 15% by weight of a hydrogen-reduced nickel powder in finely divided form is used as the auxiliary material of the alloy, although a mixture of nickel powder and iron powder comprising from 3 to 15% by weight of the composition has been found to produce a very hard and tough alloy which gives excellent results when formed as a cutting tool.

As already mentioned from 3 to 15% by weight of hydrogen-reduced nickel powder is mixed with the carbide powder; for example tantalum carbide, and this mixture is ground for about fortyeight hours in a ball mill to a very fine powder, the particles of which are thoroughly and uniformly mixed tantalum carbide and nickel.

This mixture is then subjected to a tremendous pressure, to the order of about tons per square inch, sufiicient to press the powder mixture into a body which may be handled and formed or worked to the desired shape and size. When this powder mixture has been so formed, it is heat 115 treated in a vacuum at from 1350" to 1400 C., maintained for about one hour. The resulting alloy is substantially non-porous due to the degasifying of the carbide, the thorough mixing of the very fine powders, the tremendous pressure used to press the mixture for forming prior to the heat treatment, and to the final heat treatment in the vacuum.

Thus an alloy of one or more metals of the iron group and a refractory metal carbide is formed, which has a homogeneous and substantially nonporous structure. When formed in accordance with the novel method of the invention, such an alloy retains its hardness, mechanical strength, and toughness or resistance to crumbling or breakage even at the temperature developed in its use as a cutting tool. Illustrative of the advantages of this improved method, it was found that a nickel-tantalum carbide tool formed as described above is harder and tougher than the same alloy formed by the methods known in the art, and that in taking a heavy cut on a hard manganese steel, the tool had sufficient mechanical strength to resist the reaction of the feed, was sufficiently hard to resist appreciable wear, and did not break, chip or crumble. It was also found that this tool did not heat as readily as other tools in making the cut and apparently offered a minimum resistance to the relative movement of the material being cut.

Having thus described my invention, what I claim is new and desire to secure by Letters Patent of the United States, is:

1. A method of producing a hard tantalum alloy which comprises, degasifying tantalum car- 150 bide powder at above 1600 C. in a vacuum, mixing from 85% to 97% of the degasified tantalum carbide powder with from 15% to 3% of powdered nickel and heating the mixture in vacuo to from 1350" C. to 1400 C.

2. A method of making a hard alloy having tantalum carbide as its major ingredient, but including in addition from 3% to 15% of nickel, which comprises providing a mixture of tantalum and tantalum carbide in finely divided form, mixing the finely divided tantalum and tantalum carbide with from 3% to 15% of nickel powder, and heating the mixture in vacuo to a temperature less than the melting point of the nickel, but not less than 1350 C.

3. A method of making an imporous alloy of a hard refractory metal carbide and a. softer metal having a lower melting point than the carbide metal, which comprises heating chemically combined tantalum and carbon in powder form in a vacuum to from 1600 C. to 1700 C., mixing the powder with up to fifteen percent of Search Boon nickel powder, pressing the mixture of tantalum carbide and nickel into workable bodies and heating the workable bodies in a vacuum to substantially 1350 C.

4. A method of treating metal powders in the formation of a tantalum carbide with nickel alloy to render the resulting alloy substantially non-porous, which comprises degasifying the carbon before the tantalum carbide is formed, heating the tantalum carbide powder in vacuo to about 1600 C. andheating the tantalum carbide and nickel powders in vacuo at substantially 1350 C.

5. A method of treating metal powders in the formation of a tool alloy composed substantially entirely of tantalum carbide, to render the resulting alloy substantially non-porous, which comprises degasifying the carbon at about 1500 C. before the tantalum carbide is formed, and thereafter degasifying the tantalum carbide in a vacuum at from 1600 C. to 1700 C.

CLARENCE W. BALKE. 

